A technique in which a vehicle stopped at the end of an out-of-sight road such as a curve or upslope is detected and the detection result is given to the following vehicles is useful for preventing rear-end collisions. As one such technique, a technique in which a moving vehicle is tracked and detected by using a millimeter-wave radar arranged at a road is known. In this technique, the position and velocity of a vehicle is firstly predicted according to the track data obtained in the first scanning. Then, a segmentation process and attribute generation process are performed for the obtained prediction data and the position and velocity data obtained in the second scanning, and the results are checked against each other (for example, see Patent Document 1).
The technique of tracking and detecting a moving vehicle will be further described.
In the technique of tracking and detecting a moving vehicle, a background subtraction process is firstly performed for the measurement data sent from the millimeter wave sensor. In the background subtraction process, the difference between the measurement data and the background data is calculated, and the measurement result related to a background object not to be tracked, such as a fixed structure like a utility pole or a guardrail, is deleted and the measurement data of a movement object is maintained. By performing the background subtraction process to exclude a background object from the later processes, it becomes possible to allow a longer processing time for the process of tracking and detecting a movement object, or it becomes possible to shorten the processing time.
In regard to the generation of background data, a technique is known in which background data is generated as the background data is updated by calculating a weighted average between the blurred data obtained by performing a blurring process for the measurement data and the previous background data (for example, see Patent Document 2). Moreover, a technique is known in which the updating of the background data is controlled according to a result of detecting the existence of a background object that is temporarily hidden by other objects (for example, see Patent Document 3).
In the technique of tracking and detecting a moving vehicle above, a segmentation process in which movement objects with almost the same velocity are grouped and an attribute generation process in which an attribute such as a barycenter position and a velocity of the group are calculated from the measurement data of the grouped movement objects are performed subsequent to the background subtraction process. Then, the measurement data that will be subsequently obtained for the group is predicted according to the acquired attribute, and the group is tracked by checking the prediction result against the actually acquired measurement data.
At present, the demands for road status monitoring have become more complicated in the field of road traffic management. For example, a shoulder of a road may be managed in such a manner that a shoulder lane is permitted for travel only when the traffic volume is increased on a road composed of a plurality of lanes including a shoulder lane. Alternatively, roads may be managed by adopting, for example, reversible lanes where the traveling on lanes close to the center is prohibited in a both-ways road including a plurality of lanes and then the arrangement of the centerline is changed such that traveling in the reverse direction on these lanes is allowed. Further, there are some cases in which traveling on a portion of the lanes on a road is prohibited due to traffic accidents or disabled cars. For such lanes whose use has been temporarily altered, it is desired that the monitoring be adaptable for usage on a moment-to-moment basis.
In the monitoring of lanes where vehicles are allowed to travel, the monitoring object is a vehicle as a movement object. However, vehicles may stop moving on a temporary basis due to, for example, traffic congestion or instructions given by a traffic signal, and such vehicles should be included in the monitoring object. In the monitoring of lanes where vehicles are temporarily prohibited from traveling, the monitoring object is an object existing in a lane such as a stopped vehicle, a fallen object from a vehicle, a fallen rock, and large trash, i.e., an obstruction other than a fixed structure such as a utility pole or guardrail.
If roads are monitored by using conventional road monitoring devices, it is necessary to install separate monitoring devices for such different kinds of monitoring objects as vehicles and obstructions so as to be suitable for each monitoring object.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2002-099986
[Patent Document 2] Japanese Laid-open Patent Publication No. 2000-172980
[Patent Document 3] Japanese Laid-open Patent Publication No. 2001-004742